1. Field of the Invention
This invention relates to a system for automatically measuring and monitoring systolic and diastolic blood pressure in the human body by employing non-invasive techniques.
2. Description of the Prior Art
The standard clinical method for the non-invasive measurement of blood pressure employs a device called a sphygmomanometer which comprises an inflatable cuff connected to a manometer tube in which the height of a column of mercury indicates the pressure in the cuff. The cuff is wrapped around a limb, usually the upper arm, and inflated until the pulse in the artery of the limb is suppressed because the artery is squeezed shut. The cuff is then gradually deflated, so that blood begins to flow through the artery again. The turbulent flow of the blood within the artery causes a characteristic sound known as a Korotkoff sound of K-sound. The pressure indicated by the manometer at that instant corresponds to the systolic blood pressure. With further deflation of the cuff, the turbulent flow in the now fully opened artery becomes so-called "laminar flow" and the sound ceases. The pressure measured at that instant corresponds to the diastolic blood pressure.
There are any number of prior art devices which have automated the procedure described above. Typically, these blood pressure measuring systems consist of a microphone for sensing Korotkoff sounds, a cuff pressurization source, electronic circuitry for processing Korotkoff sounds, and a technique for displaying systolic and diastolic blood pressure values.
Typically, an automated blood pressure instrument is preset during manufacture to inflate to a maximum cuff pressure that is above the maximum expected pressure. In this case, the applied pressure is determined by the patient with the highest expected pressure. Some machines have the ability to remember previous pressure readings from the same patient. In these machines, the problem of maximum cuff pressure is reduced when the instrument is dedicated to successive measurements even through "first readings" must often be disregarded. Other machines inflate to a typical maximum value; if shown to be inadequate, they will then modify the inflation cycle to automatically re-inflate to a higher pressure.